A machine tool such as a lathe conventionally includes a fixing device (hereinafter referred to as a chucking device), which fixes a workpiece such as a round bar in a main spindle.
The chucking device includes a fixing section which rotates with a main spindle, fixes a workpiece in a closed state, and releases the fixation of the workpiece in an open state, an actuating lever which rotates with the main spindle, and is displaced so as to open and close the fixing section, and a sliding member which is provided to be movable between the first position and the second position along the axis direction of the main spindle, rotates with the actuating lever while displacing the actuating lever in contact therewith in the second position in the movable range, and does not have contact with the actuating lever in the first position.
The fixing section is closed when the sliding member is in the second position and the fixing section opens when the sliding member is in the first position.
The sliding member hardly rotates when the sliding member does not have contact with the actuating lever, or the sliding member rotates by accompanying rotation owing to slight contact with the outer circumferential surface of the main spindle. For this reason, the difference between the rotation of the sliding member and the rotation of the actuating lever rotating with the main spindle is increased, resulting in a problem in that the sliding member becomes worn away in the rotation direction due to such a large difference in rotation speeds when the sliding member has contact with the actuating lever.
It is therefore proposed to always rotate the sliding member integrally with the main spindle by providing a brake member between the sliding member and the main spindle in order to avoid relative movement between the sliding member and the main spindle (Patent Document 1).
With this technique, the sliding member always rotate integrally with the main spindle by the brake member provided between the main spindle (spindle in Patent Document 1) and the sliding member (shifter in Patent Document 1). On the other hand, the actuating lever (chuck claw) always rotates integrally with the main spindle, so that the rotation speeds of both of the sliding member and the actuating lever are the same when the sliding member has contact with the actuating lever. Therefore, the wear in the rotation direction can be prevented or controlled because the sliding member and the actuating lever do not have a difference in speeds.